Target data

The parameters specified below define the target position and rotator position angle.

Target name and position

in any of the coordinate systems supported by the WHT telescope control system. The following parameters are required:

Right ascension

Hours, minutes, seconds, separated by spaces.

Declination

Degrees, minutes, arcseconds, separated by spaces.

Equinox

Mean FK4 or FK5 systems (e.g. B1950, J2000) or apparent coordinates of arbitrary date. (Note that this is a change from the WHT TCS, which supports apparent coordinates of current date only. This is necessary in order to allow running of the guide star search software well before the observations take place).

The remaining parameters are optional. Parallax and radial velocity, in particular, will make very small differences to the exact selection of guide stars and to the computed guide probe positions, but are retained for consistency with the TCS and to allow direct use of WHT catalogue files.

Proper motions

in RA (seconds of time per year) and Dec (arcseconds per year). Defaults to zero.

Epoch

(year). Defaults to equinox.

Parallax

(arcsec). Defaults to zero.

Radial Velocity

(kms$-1$; defaults to zero).

It is possible to input target positions in a catalogue file in the format accepted by the WHT control system. In this case, references to a particular object are by name. The catalogue format is described in detail in Section 7.1.

Rotator position angle

This is a sky position angle, in the range $0o$ - $360o$, as used by the relevant telescope control system. See Appendix A.2 for some subtleties affecting wide fields.